Method of forming a visual record of a latent image on an image receiving web



Oct. 25, 1966 v. s MIHAJLOV 3,281,241

METHOD OF FORMING A VISUAL RECORD OF A LATENT IMAGE ON AN IMAGE RECEIVING WEB Filed July 2, 1962 mUmDOm MO HJO TS wl INVENTOR. VSEVOLOD S. MIHAJLOV ATTORNEY United States Patent O 3 281 241 METHOD OF FORMIN G A VISUAL RECORD OF A LATENT IMAGE ON AN IMAGE RECEIVING York Filed July 2, 1962, Ser. No. 206,987 15 Claims. (Cl. 96-1) This invention relates to xerography and in particular to the production of visible records of an electrostatic image.

The production of copies of drawings, documents, or printed matter by electrostatic processes is now well known. According to one method a latent electrostatic image formed on a reusable non-conductive support is rendered visible by dusting with finely divided oppositely charged toner particles. This toner image may then be transferred to an image receiving websuch as ordinary paper and fixed thereon by heat fusing or the like.

Although developing techniques employing dry developers, such as cascade development, magnetic development and the like, are well known and characterized by many advantages, electrostatic processing is not necessarily limited thereto. Liquid development techniques have also been successfully employed and are of particular importance because of the generally high degree of image resolution obtainable thereby. Liquid development also provides more complete coverage of solid area images, as distinct from line copy, than is ordinarily obtainable with dry developer systems without special control elements.

Various methods involving the use of liquid developer are known. For instance, the liquid immersion method comprises immersing the plate supporting an electrostatic image into a developer made up of finely divided particles suspended in an insulating liquid. Either the charged or the uncharged areas of the plate are developed as desired depending upon the polarity of the charge on the particles. Image resolution as high as 600 lines per mm. has reportedly been attained by this method and although image quality is generally superior there are distinct disadvantages inherent in the immersion method. In particular, it normally involves the handling of fairly large quantities of frequently volatile and sometimes toxic liquids. Also it has been found that images developed by this method are not readily transferable by conventional methods.

Another liquid development method comprises pouring the developer across the charged and exposed plate. Generally good results are attainable, but the disadvantages already mentioned are applicable. In addition, this technique is rather sloppy. Still another method of liquid development comprises rolling a plate bearing an electrostatic charge pattern across a roller which is partially immersed in developer. The roller serves as a means to transfer the developer from a supply tank to the plate and at the same time, may act as an electrode. Again, the disadvantages of handling large quantities of liquid and the inconvenience of transfer are present.

Now in accordance with the present invention a visible record of an electrostatic image may be formed directly on an image receiving web by a liquid development tech nique from which the disadvantages commonly associated with liquid development have been eliminated. The present invention not only obviates the usual separate transfer step, it also provides for the production of multiple copies from a single electrostatic image.

Briefly this invention, described in detail below, comprises placing a small quantity of liquid developer containing dye particles, charged to the same polarity as the image to be developed, near the edge of a plate supporting a latent electrostatic image. Successive portions of an image receiving material .are then brought into close cont-act with successive portions of the plate while a bead of developer is advanced in front of the leading edge of the paper as it comes into contact with the plate. A visible record of the image is thereby produced directly on the receiving material. By merely repeating these steps, additional copies conforming to the charge pattern may be made.

Accordingly, the principal object of this invention is to provide a novel method for producing a visible record conforming to a latent electrostatic image.

Another object of this invention is to provide a novel method to develop the copy of an electrostatic image directly on an image receiving web.

Another object of this invention is to provide a liquid development system for producing multiple copies from an electrostatic image.

Still another object of this invention is to provide a liquid development system requiring the handling of only small quantities of liquid thereby reducing the expense, minimizing vapors released, and inconvenience commonly associated with liquid development.

In the following detailed description 'of this invention, reference is made to the accompanying drawings in which:

FIGURE 1 is an isometric view of a layer developable in accordance with this invention;

FIGURE 2 is a schematic representation of liquid development according to the present invention;

FIGURE 3 is an isometric view illustrating the instant liquid development method.

Illustrated in FIGURE 1 is an image system applicable to the present invention. Latent electrostatic image 11 on the surface of insulating plate 12 is designated by the plus marks and for purposes of this description is assumed to be of positive polarity. However, it is to be understood that the latent image may be of either positive or negative polarity and may consist of gradations of potential or charge or may be as illustrated in the figure areas of charge interspaced by areas of substantially no charge. The particular image illustrated in FIGURE 1 may be regarded as a line copy image consisting of representative areas of charge and absence of charge which desirably can be printed as areas of black on a white surface. Insulating plate 12 must be at least sufiiciently non-conductive to support an electrostatic charge during the instant process. The conventional xerographic plate is suitable for this purpose, but it is not suggested that this invention is limited thereto.

FIGURE 2 is a schematic representation of the present invention. To more clearly present the invention, FIG- URE 2 has been broken up into three parts: (a), (b) and (c). In 2(a) there is shown an image system with developer, image receiving web and roller positioned as at the beginning of the instant process; FIGURE 2(b) shows the system with the roller rolled part way across the insulating plate; and in 2(0) is shown the system at the completion of the instant process. Each component appearing in more than one view has been assigned the same numerical designation in all views in which it appears. Plus marks designate latent electrostatic image 11 on or near the surface of insulating plate 12. As shown in FIGURE 2(a) at the start of the printing process pressure roller 13 is positioned on the surface and near one edge of plate 12; image receiving web 14 is positioned at an angle in such manner that its leading edge rests on plate 12 immediately adjacent to and on the image side of roller 13; a bead of developer 15 is placed on the surface of plate 12 'between said leading edge of web 14 and said image 11.

The liquid developer employed in the present invention is described in detail below. It preferably comprises finely divided electrically charged dyestufl", herein termed toner, dispersed in a relatively non-conductive liquid carrier. For purposes of this description, the toner is assumed to be charged to the same polarity as that of latent electrostatic image 11.

As illustrated in view 2(b) pressure roller 13 is then rolled in the direction indicated by the arrow so that successive portions of web 14 are brought into intimate contact with successive portions of plate 12. The lateral movement of roller 13 advances developer 15 across the surface of plate 12 in front of the pressure line created by roller 13. Successive portions of web 14 are preferably separate from plate 12 after having been brought into intimate contact by the action of pressure roller 13.

From results obtained following the procedures described it is believed that as developer 15 travels across latent image 12, electrical forces impel the suspended charged toner particles onto image receiving web 14 forming a visible toner image 17 thereon as shown in FIGURES 2(b) and 2(0). In non-image areas, where there are no electrical forces to so impel toner particles, the particles remain in suspension and are simply moved along by the viscous drag of the suspending medium of developer 15. The effect is to produce clean copy devoid of background and including particles and clearly discernible and dense images in areas conforming to areas of charge in the latent image.

Roller 13 desirably comprises an electrically conductive material, such as conductive rubber. However, other materials including non-conductive materials may also be used. When a conductor is employed, print quality is enhanced by applying an electrical potential to the roller. Relatively small quantities of toner may adhere to the image receiving material in non-image areas thereby causing the appearance of background in the prints if the roller is allowed to electrically float. This undesired phenomenon can be appreciably reduced by app-lying an electrical potential of the same polarity as that of the toner to roller 13. Of course, the magnitude of this electrical potential must not be so great as to prevent deposition of toner in image areas. Generally this potential is between about ground and about the potential of the discharge areas of the surface bearing the charge pattern.

Illustrated in FIGURE 3 is visible toner image 17 adhering to web 14 in conformity with electrostatic image 11. If desired, toner image 17 may be rendered permanent by an appropriate method such as pressure fixing, heat fusing or the like. Alternatively a liquid developer may be employed which is self-fixing. The various usable known developers are discussed below.

Since the described process does not apparently discharge the latent electrostatic image 11, this process is suitable for the production of multiple copies. Copies of substantially uniform quality may be made from an electrostatic charge patternby merely repeatedly carrying out the process described in connection with FIG- URES 2(a), (b) and (c).

Several different materials have been tried and found suitable for use as the image receiving web in the production of copies according to the instant invention. Electrically conductive as well as electrically non-conductive materials including various bond papers, barytacoated papers, plastic films such as Mylar film and Saran film, steel and brass foil, aluminum and paper multilith masters as well as very thin aluminum foil have been used successfully. Bond paper because of its absorbent characteristics was found to produce prints with considerable background. It is believed that the coarse surface of bond paper is another detrimental factor because of a tendency to entrap toner particles in non-image areas. Higher quality, relatively background-free prints can be made on smoother, less absorbent materials such as, for example, baryta-coated paper.

An unexpected phenomenon was found to be associated with the use of very thin aluminum foilas the image receiving web. In addition to the toner image produced on the side of the foil which was brought into contact with the electrostatic image, the opposite side of the foil was deformed or raised in conformity with areas developed. This deformation elfect might be attributable to electrical field forces created by the electrostatic image which impel the toner particles onto the very thin metallic foil.

Developer compositions suitable for use in the present invention comprise dispersions of toner particles formed in a liquid carrier, for example, by stirring or other methods Well known to those skilled in the art. It is understood that the toner particles may be liquids, solids or organosols capable of being dispersed in the carrier. Thus, suitable dispersions, suspensions and emulsions and other collodial systems are within the scope of this invention.

The carrier liquid must be a highly insulating material, preferably with a volume resistivity of at least about 10 ohm centimeters, in order to avoid discharge of the latent electrostatic image. Suitable liquids include hydrocarbons such as benzene, xylene, hexane, naphtha, cyclohexane, etc; halogenated hydrocarbons such as carbon tetrachloride, trichloroethylene, chloroform, Freons (a trade name of E. I. du Pont de Nemours & Co. for various fluorinated compounds), Genetrons (a trade name of Allied Chemical Co. for various fluorinated compounds), etc.; miscellaneous liquids such as silicone liquid, turpentine, etc. A particularly useful material of refined petroleum hydrocarbon class is Sohio Odorless Solvent (SOS) sold by the Standard Oil Company of Ohio. Suitable viscosity agents such as parafiin wax, liquid petrolatum, etc., may be added to increase the viscous drag of the carrier.

Liquid toner particles mus-t be substantially immiscible with the carrier liquid and capable of \being dispersed in the form of very small droplets. An almost limitless number of suitable materials exist which may be used in conjunction with the present invention. One suitable class of materials comprises aqueous inks such as ordinary commercial fountain pen inks. Another particularly useful class of materials includes glycols, preferably including soluble dyes in order to render the image visible. Particularly suitable examples include ethylene glycol sontaining about 5% of crystal violet of malachite green Suitable solid toner particles include pigments, dyes, resins, metals, and materials such as charcoal and graphite and similar material, having a fine particle size and being insoluble in the carrier liquid. In general, the finer the powder the better the grain in the developed image. It is preferred that the average particle size be no larger than about 20 microns and for high quality work, it is preferred that the average particle size be no more than about 5 microns.

As mentioned above, the toner image is typically rendered permanent by a separate fixing step such as heat fusing or the like. If desired, the separate fixing step may be obviated by an appropriate selection of developer components. For instance, self-fixing characteristics may be imparted to the developer by using toner particles comprising resins which are binders or film-forming. A composition suitable for this purpose comprises an organosol in which a solution of a resin binder in a polar solvent is dispersed in a non-polar carrier. Another suitable composition comprises a suspension of finely divided resin dyes-tufi? in molten parafi'in wax. solidification of the wax upon cooling to room temperature serves to fix the image to the image receiving web.

It has been found that roller pressure may vary over a wide range without deleteriously affecting image production. Of course, it is necessary that sufiicient pressure be exerted to bring the image receiving Web into intimate contact with the plate supporting the electrostatic image and to cause the developer to travel across the plate so that it will be brought into operative proximity with the electrostatic charge and the image receiving web.

It has also been found that reversal development, or deposition conforming to uncharged areas, may be accomplished by using a suitable toner which is oppositely charged with respect to the electrostatic image on the plate. For such applications of the instant invention, it is desirable to apply an electrical potential to the pressure roller opposite in polarity to the charge of the toner. As indicated above, the electrical bias applied to the roller may again be selected to influence both image density and background density of the prints.

For an example of proper selection of the variables discussed, good quality line copy prints may be made according to the instant invention on baryta-coated paper from an electrostatic image of positive polarity varying over a range of a maximum of about 600 volts and a minimum of about ground by using approximately 0.2 ml. of a developer comprising by weight of toner suspended in a suspending medium comprising paraffin wax and Sohio Odorless Solvent, applying a positive electrical bias of the order of about 100 volts to the pressure roller, and using a roller speed in the order of 3040 seconds per pass over a 4 x 5 inch plate.

Limitation by the specific embodiments of the invention as set forth in this application is not intended. Rather, it is intended that the claims apply broadly within the spirit and scope of this invention.

What is claimed is:

1. The method of forming on an image receiving web a visual record of a latent electrostatic image on an image support member comprising placing an individual droplet of developer comprising particulate electrical-1y charged toner suspended in a non-conductive liquid carrier on said image support member, simultaneously establishing a line of intimate physical contact between successive portions of said image receiving web and said image support member and advancing said line, said developer advancing in front of said line of intimate physical contact and between said image receiving web and said image support member to deposit said toner particles on said image receiving web in image configuration at said line of intimate physical contact, and separating said web from said image support member bearing a developed image.

2. The method of depositing toner particles on an image receiving web in conformity with a latent electrostatic image on an image support member comprising placing an individual droplet of developer comprising electrically charged toner particles suspended in a non-conductive liquid carrier onto said support member, bringing successive portions of said web into intimate contact with successve port-ions of said support member by rolling a cylindrical roller across said web and simultaneously advancing said developer before the line of contact between said web and said support member, and separating said web from said image support member.

3. A method for forming on an image receiving web a visual record of a latent electrostatic image on an image support member comprising advancing developer comprising electrically charged toner particles suspended in a non-conductive liquid carrier across said support member by establishing a line of intimate physical contact between successive portions of said web and said support member whereby toner particles are selectively deposited on said web in image configuration, and separating said web from said support member.

4. The method according to claim 2 wherein said roller is electrically conductive.

5. The method according to claim 2 wherein said roller is electrically conductive and an electrical bias is applied to said roller.

6. The method according to claim 2 wherein said roller is electrically conductive and wherein an electrical potential equal to the maximum potential of said latent electrostatic image is applied to said roller.

7. The method according to claim 1 wherein said liquid carrier is a refined petroleum hydrocarbon having a resistivity of at least about 10 ohm centimeters.

8. The method according to claim 1 wherein said particulate toner comprises finely divided powder particles the average size of which particles is no larger than about 20 microns.

9. The method according to claim 1 wherein said particulate toner comprises a solution of resin in a solvent therefor and said liquid carrier comprises a non-polar organic liquid.

10. The method according to claim 1 wherein said toner particles deposited on said image receiving web are fixed thereto by heat fusing.

11. The method according to claim 1 wherein said particulate toner comprises a solution of resin in a solvent therefor and including the additional step of fixing said toner particles deposited on said image receiving web by eliminating the solvent therefrom.

12. A method for xerographic image reproduction comprising applying an electrostatic charge of one polarity to the surface of a xerographic plate, exposing said plate to a pattern of light and shadow, placing an individual droplet of developer comprising electrically charged particles suspended in a nonconductive liquid carrier on the said plate, establishing a line of intimate physical contact between successive portions of said plate and an image receiving web and advancing said developer in front of said line of contact whereby printing of a visible record of said latent electrostatic image is elfected on said web, and separating said web from said xerographic plate.

13. The method of developing a visible record of a latent electrostatic image residing on an image support member comprising:

(a) establishing a line of intimate contact between a leading area of an image receiving web and the image support member at an individual bead of liquid developer on said image support member;

(b) advancing said line of intimate contact (1) to establish pressure contact between successive areas of said web and said image support member, and,

(2) to distribute and move said liquid developer across the surface of said support member in advance of said line of intimate contact; and,

(c) separating successive areas of said web from said support member;

wherein said liquid developer comprises electrically charged particulate toner suspended in a non-conductive liquid carrier.

14. The method of producing a visible record of a latent electrostatic image formed on an image support member, including:

(a) contacting a leading area of a first surface of a very thin aluminum foil with the image support member at an individual head of liquid developer comprising electrically charged toner particles suspended in a nonconductive liquid carrier on said member;

(b; llnoving a roller across a second surface of said (1) to establish contact between successive areas of the first surface of said foil and said support member, and,

(2) to move said developer across said image support member in advance of said areas of said foil successively contacted with said support member; and,

(c) separating successive areas of said foil from said support member;

whereby said foil is deformed in conformity with said electrostatic image.

15. The method accord-ing to claim 14 wherein an electrical potential is applied between said roller and said image support member as said roller is moved across References Cited by the Examiner UNITED STATES PATENTS 8/1958 Walkup 961 8/1959 Straughen 96-1 8 Metcalfe et a1 961 Land et a1 96-29 Bixby 961 Heckscher 961 Hunter 117-175 NORMAN G. TORCHIN, Primary Examiner.

A. LIBERMAN, D. D. PRICE, Assistant Examiners. 

1. THE METHOD OF FORMING ON AN IMAGE RECEIVING WEB A VISUAL RECORD OF A LATENT ELECTROSTATIC IMAGE ON AN IMAGE SUPPORT MEMBER COMPRISING PLACING AN INDIVIDUAL DROPLET OF DEVELOPER COMPRISING PARTICULATE ELECTRICALLY CHARGED TONER SUSPENDED IN A NON-CONDUCTIVE LIQUID CARRIER ON SAID IMAGE SUPPORT MEMBER, SIMULTANEOUSLY ESTABLISHING A LINE OF INTIMATE PHYSICAL CONTACT BETWEEN SUCCESSIVE PORTIONS OF SAID IMAGE RRECEIVING WEB AND SAID IMAGE SUPPORT MEMBER AND ADVANCING SAID LINE, SAID DEVELOPER ADVANCING IN FRONT OF SAID LINE OF INTIMATE PHSYICAL CONTACT AND BETWEEN SAID IMAGE RECEIVING WEB AND SAID IMAGE SUPPORT MEMBER TO DEPOSIT SAID TONER PARTICLES ON SAID IMAGE RECEIVING WEB IN IMAGE CONFIGURATION AT SAID LINE OF INTIMATE PHYSICAL CONTACT, AND SEPARATING SAID WEB FROM SAID IMAGE SUPPORT MEMBER BEARING A DEVELOPED IMAGE,
 14. THE METHOD OF PRODUCING A VISIBLE RECORD OF A LATENT ELECTROSTATIC IMAGE FORMED ON AN IMAGE SUPPORT MEMBER, INCLUDING: (A) CONTACTING A LEADING AREA OF A FIRST SURFACE OF A VERY THIN ALUMINUM FOIL WITH THE IMAGE SUPPORT MEMBER AT AN INDIVIDUAL BEAD OF LIQUID DEVELOPER COMPRISING ELECTRICALLY CHARGED TONER PARTICLES SUSPENDED IIN A NONCONDUCTIVE LIQUID CARRIER ON SAID MEMBER; (B) MOVING A ROLLER ACROSS A SECOND SURFACE OF SAID FOIL, (1) TO ESTABLISH CONTACT BETWEEN SUCCESSIVE AREAS OF THE FIRST SURFACE OF SAID FOIL AND SAID SUPPORT MEMBER, AND, (2) TO MOVE SAID DEVELOPER ACROSS SAID IMAGE SUPPORT MEMBER IN ADVANCE OF SAID AREAS OF SAID FOIL SUCCESSIVELY CONTACTED WITH SAID SUPPORT MEMBER; AND, (C) SEPARATING SUCCESSIVE AREAS OF SAID FOIL FROM SAID SUPPORT MEMBER; WHEREBY SAID FOIL IS DEFORMED IN CONFORMITY WITH SAID ELECTROSTATIC IMAGE. 